Now on that occasion the venerable Sāriputta was standing behind the Blessed One, [501] fanning him. Then he thought: “The Blessed One, indeed, speaks to us of the abandoning of these things through direct knowledge; the Sublime One, indeed, speaks to us of the relinquishing of these things through direct knowledge.” As the venerable Sāriputta considered this, through not clinging his mind was liberated from the taints.

MA: Having reflected on the discourse spoken to his nephew, Ven. Sāriputta developed insight and attained arahantship. Dı̄ghanakha attained the fruit of stream-entry.

“Again, bhikkhus, by completely surmounting the base of neither-perception-nor-non-perception, Sāriputta entered upon and abided in the cessation of perception and feeling. And his taints were destroyed by his seeing with wisdom.

MA offers this explanation of the passage, transmitted by “the elders of India”: “The Elder Sāriputta cultivated serenity and insight in paired conjunction and realised the fruit of non-returning. Then he entered the attainment of cessation, and after emerging from it he attained arahantship.”

But in the wanderer Dīghanakha the spotless immaculate vision of the Dhamma arose: “All that is subject to arising is subject to cessation.” The wanderer Dīghanakha saw the Dhamma, attained the Dhamma, understood the Dhamma, fathomed the Dhamma; he crossed beyond doubt, did away with perplexity, gained intrepidity, and became independent of others in the Teacher’s Dispensation.

MA: Vision of the Dhamma (dhammacakkhu) is the path of stream-entry. The phrase “All that is subject to arising is subject to cessation” shows the mode in which the path arises. The path takes cessation (Nibbāna) as its object, but its function is to penetrate all conditioned states as subject to arising and cessation.

Thanissaro Bhikkhu wrote:Sometimes non-reactivity gets inserted into the path under the factor of right mindfulness. But the Buddha never defined mindfulness as non-reactivity. Mindfulness in his lexicon means the ability to keep something in mind. And there is such a thing as right mindfulness and wrong mindfulness. Wrong mindfulness is when you keep in mind desires that get you worked up about the world. Right mindfulness is when you take any of four frames of reference and keep them in mind as a basis for right concentration.

Now, when the Buddha teaches concentration, he does start out with non-reactivity or equanimity as a prerequisite. Before he teaches Rahula breath meditation, he tells him first to make his mind like earth. When disgusting things are thrown on the earth, the earth doesn't react. Then he adds, "Make your mind like water. Water doesn't get disgusted when it has to wash away disgusting things. Make your mind like fire. Fire doesn't get disgusted when it burns disgusting things. Make your mind like wind. Wind doesn't get disgusted when it blows disgusting things around." You try to make your mind imperturbable like the elements.

So here there would be an element of non-reactivity. But this non-reactivity is for the purpose of putting your mind in a position where it can observe things clearly, and in particular, to observe your actions and their results in a patient, reliable way. Because when you start working with the breath, you're not just looking at the breath in a nonreactive way. You're working with it, playing with it, mastering it through experimenting with it. And you want to be able to judge the results of your experiments in a fair and accurate manner (http://www.accesstoinsight.org/lib/auth ... sntnibbana).